Show that the expansion of does not contain any term involving x9.
For ,
a=2x2, and n=20
We have a formula,
To get coefficient of x9 we must have,
(x)40-3r = (x)9
• 40 - 3r = 9
• 3r = 31
• r = 10.3333
As is not possible
Therefore, the term containing x9 does not exist in the expansion of